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Cancer treatment response may be affected by gut bacteria

The news comes from research into whether people with cancer might respond differently to cancer treatment depending on the bacteria in their gut.

Researchers specifically looked at a type of cancer treatment called immunotherapy.

This involves stimulating the immune system to attack cancerous cells - in this case, by using specially engineered antibodies known as monoclonal antibodies.

Some people respond better to this treatment than others. The researchers wanted to see if the make-up of gut bacteria influenced the outcome of treatment.

The study involved looking at the gut bacteria of 249 people who'd received immunotherapy for different types of cancer, some of whom had also taken antibiotics.

Researchers found gut bacteria differed between people who responded well to immunotherapy and those who didn't.

People who had a positive response tended to have more of a bacteria called Akkermansia muciniphilia.

Transplanting gut bacteria from these people into mice with tumours seemed to improve cancer outcomes in the mice.

The researchers also observed that both people and mice with cancer who'd been given antibiotics tended to have poorer cancer outcomes.

But this research is in its very early stages and the reasons behind these observations are unknown.

We're a long way from being able to say categorically that our gut bacteria directly affect how we respond to treatments, or whether altering the gut bacteria could boost people's responses to immunotherapy.

Where did the story come from?

The study was carried out by researchers from a number of research institutions in France, including Gustave Roussy Cancer Campus, Nationale contre le Cancer, Université Paris-Sud and Université Paris-Saclay, as well as the Memorial Sloan Kettering Cancer Center and Weill Cornell Medical College in the US, and Karolinska University Hospital in Sweden.

The researchers were funded by grants from a range of organisations.

The study was published in the peer-reviewed journal Science.

The story was covered well by BBC News, with accurate reporting of the details of the research and appropriate cautions from experts about how we interpret the results.

What kind of research was this?

The research involved several studies, including laboratory experiments, that aimed to see whether bacteria present in the gut may affect how people respond to certain types of cancer treatment.

Treatments that target aspects of the immune system, such as specially engineered antibodies know as monoclonal antibodies, can be effective for certain types of cancer, including advanced malignant melanoma or lung cancer.

But the cancers are resistant to these treatments in around two-thirds of people.

The researchers wanted to see whether gut imbalance as a result of cancer or antibiotic use could affect how people respond to treatment.

They looked at mice with tumours and whether giving antibiotics to people with cancer affected their response to cancer treatment.

These are only very early-stage studies, so there aren't any definitive answers at this stage.

What did the research involve?

The researchers first tested how effective 2 types of immunotherapy were in mice with either sarcoma (cancers of bone, muscle and connective tissue) or melanoma (aggressive skin cancer). Some of the mice were also given antibiotics.

They then looked at 249 people with an advanced form of the most common type of lung cancer (non-small cell), cancer of the kidney (renal cell), or cancer of the bladder or ureters (urothelial carcinoma).

The researchers noted whether people had received antibiotics (for example, for a dental infection) either 2 months before or 1 month after starting immunotherapy, and whether this affected their response to immunotherapy.

The researchers then looked at the specific microbes found in the guts of 100 of the people in the study using DNA sequencing.

They also looked at whether mice treated with antibiotics could have an improved response to immunotherapy if they received a stool transplant from people in the study.

What were the basic results?

The results of the different studies were as follows:

Mice with melanoma or sarcoma that were treated with antibiotics were less likely to survive after immunotherapy compared with those who weren't treated with antibiotics.

People who took antibiotics around the time they started immunotherapy had less positive outcomes from their cancer treatment than those who didn't take antibiotics (lower rates of overall survival and lower rates of survival without cancer progression).

People who responded well to treatment were more likely to have a particular bacteria called Akkermansia muciniphila in their gut.

Mice given stool transplants from people who responded well to immunotherapy had slower-growing tumours than those who had transplants from people who had a poor response.

How did the researchers interpret the results?

The researchers concluded the study showed that gut microbes impacted the response people had to cancer treatment.

They acknowledged, however, it wasn't clear exactly how the microbes influenced people's responses to treatment with immunotherapy with monoclonal antibodies.

Conclusion

This early-stage study gives us some insights into factors that might influence people's responses to a specific type of cancer treatment (immunotherapy with monoclonal antibodies).

The findings are of interest, but don't have any immediate implications for cancer treatment.

We don't know what the conditions that required antibiotic treatment were and whether these could have affected the response to immunotherapy.

We don't know whether the antibiotics themselves influenced how well the immunotherapy worked, or whether it was their effect on gut bacteria.

We also don't know whether having high levels of particular bacteria improves people's responses to immunotherapy, or whether the immunotherapy somehow influences the levels of specific bacteria.

It's unclear whether the findings are more relevant to certain cancers or specific immunotherapies or antibiotic types, or if they're influenced by other patient characteristics.

Further research first needs to clarify whether the gut bacteria directly influences people's responses to immunotherapy, and exactly how this happens.

The next step would be to investigate whether treatment to change the gut bacteria could improve people's responses to cancer treatment.

Overall, it's likely to be some time before we see whether this early study eventually leads to any changes in the way immunotherapy is given.

These findings shouldn't cause any concern for people with cancer who need to take antibiotics.

The risk of not taking the antibiotics you need to treat an infection is likely to be far greater than any potential effect the medicines may have on the cancer or how you respond to treatment.

Summary

"Gut bacteria 'boost' cancer therapy," BBC News reports. The news comes from research into whether people with cancer might respond differently to cancer treatment depending on the bacteria in their gut...

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